Most of the action in the plot of this play is derived from the malicious intrigues of Don John. He is the bastard brother of Don Pedro, Prince of Arragon, against whom he had recently led an unsuccessful rebellion.

As the victor, Pedro has forgiven him, and John accepts the gestures of reconciliation as a temporary expedient, while rooting out opportunities to effect his revenge.

Antagonisms between a 'legitimate' and 'illegitimate' brother exist not only in the relationship of Don John and Don Pedro, but also between Edgar and Edmund in King Lear and between Robert Faulconbridge and Philip, the Bastard. (Thersites as a bastard stands alone.)

Whereas Faulconbridge and Thersites both show a resigned acceptance to their condition, Don John, like Edmund, is consumed by a festering resentment which motivates their negative actions.

Following the climax of John's wicked mischief, Benedick says of him:

"The practice of it lives in John the bastard,
Whose spirits toil in frame of villainies."
Act IV sc. i

But what does John think of himself? He tells us in a dialog with his henchman,
Conrade:

Conrade: "What the good-year, my lord! why are you thus out of measure sad?"

Don John: "There is no measure in the occasion that breeds; therefore the sadness is without limit."

Conrade: "You should hear reason."

Don John: "And when I have heard it, what blessing brings it?" Conrades "If not a present remedy, at least a patient sufferance." Don John " I wonder that thou, being ( as thou sayest thou art) born under Saturn, goest about to apply a moral medicine to a mortifying mischief, I cannot hide what I am: I must be sad when I have cause, and smile at no man's jests; eat when I have stomach, and wait for no man's leisure; sleep when I am drowsy and tend on no man's business; laugh when I am merry and claw no man in his humor."

Conrade: "Yea, but you must not make the full show of this till you may do it without controlment. You have of late stood out against your brother, and he hath ta'en you newly into his grace; where it is impossible you should take true root but by the fair weather that you make yourself: it is needful that you frame the season for your own harvest."

Don John: "I had rather be a canker in a hedge than a rose in his grace; and it better fits my blood to
be disdained of all than to fashion a carriage to rob love from any: in this, though I cannot be said to be a flattering
honest man, it must not be denied but I am a plain-dealing villain. I am trusted with a muzzle, and en-franchised with a clog; therefore I have decreed not to sing in my cage. If I had my mouth, I would bite: if I had my liberty, I would do my liking:
in the meantime let me be that I am, and seek not to alter
me." Act I sc.iii

When his conspiracy is at last discovered and put to rights, he takes to the hills,
but we are assured by a messenger at the end of the play that he has been caught and brought back to Messina, where
Benedick, the hero, promises a just punishment for him. But there is no promise
that it will either reform or change him.